IFN-associated B cell hyperactivity is highly enriched in SLE patients harboring Sm/RNP antibodies.

Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by an array of autoantibodies, in particular anti-nuclear antibodies (ANA). The disease is also hallmarked by an expansion of plasmablasts (PB) in peripheral blood. How these relate to autoantibody production is not clear. Here, we aimed to understand B cell alterations in SLE and their relationship to immunoglobulin levels and autoantibody production. We demonstrate that a subgroup of SLE patients is characterized by a high frequency of PB relative to memory B cells (high PB/M). Patients with this phenotype more frequently had high disease activity. Despite low overall frequencies of memory B cells, these patients exhibited an increased activation in the switched CD27+ memory compartment and a strong IFN signature in PB. Repertoire analysis revealed a highly polyclonal expansion and enrichment for IgG1 expressing PB in patients with a high PB/M ratio which was reflected in increased serum IgG levels. Importantly, the hyperactive B cell phenotype was highly enriched in patients harboring Sm/RNP autoantibodies (OR: 9.17 (2.97-26.0)). In summary, we show for the first time a direct relationship between IFN and PB expansion in a subgroup of SLE patients, highly enriched in those harboring Sm/RNP antibodies. These results provide insight into the pathways leading to B cell hyperactivity and autoantibody production which may guide the tailoring of B cell- and IFN-targeted therapies.